The evolution of the autonomic nervous system provides an organizing principle to interpret
the adaptive significance of physiological responses in promoting social behavior.
According to the polyvagal theory, the well-documented phylogenetic shift in neural
regulation of the autonomic nervous system passes through three global stages, each with
an associated behavioral strategy. The first stage is characterized by a primitive
unmyelinated visceral vagus that fosters digestion and responds to threat by depressing�…